Build out examples/documentation for unit testing Workflows/activities

[daanschutte]

Description

Improves testing examples for Dapr Workflows by adding test coverage for additional concepts and fixing documentation issues.

• Changes to the README:
  • Corrected the port to match the default
  • Reordered startup sequence to prevent launch errors (start Dapr sidecar before program)
  • Added a table to expand on which concepts are tested
• Added more tests
  • TestHighCostOrderApproved: Mock external events (WaitForExternalEventAsync) and verify custom status
  • TestHighCostOrderApprovalTimeout: Simulate timeouts with TaskCanceledException
  • TestActivityException: Simulate activity failures with WorkflowTaskFailedException
• Dropped unused test file

Issue reference

Addresses #1532 by improving test coverage. Additional improvements may be needed - open to suggestions.

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation